An immunohistochemical demonstration of gastrin-releasing peptide (GRP) in the rat substantia nigra.

The presence of gastrin-releasing peptide-like immunoreactivity in the rat brain was investigated by use of the indirect peroxidase-antiperoxidase technique. A high density of gastrin-releasing peptide-like immunoreactive terminals in the ventral pallidum, the interpenduncular nucleus and in substantia nigra, pars reticulata, was observed. Moreover, gastrin-releasing peptide-like immunoreactive perikarya were observed in the hypothalamic suprachiasmatic nucleus. Antisera raised against gastrin-releasing peptide have been shown to cross-react with substance P, another peptide highly concentrated in the substantia nigra, the ventral pallidum and the interpenduncular nucleus, and gastrin-releasing peptide-immunoreactivity in these areas has therefore been regarded as substance P immunoreactivity. To determine the antigenic epitope recognized by the antiserum raised against gastrin-releasing peptide, specificity studies were performed with known peptides fixed to nitrocellulose filter strips as well as preabsorptions with the same peptides on fixed brain sections containing the substantia nigra. From these experiments, it could be deduced that the antiserum recognizes an epitope within the peptide sequence: Val-Gly-His-Leu-Met-NH2. The antiserum cross-reacts with bombesin and alytesin, but not with substance P, allowing us to conclude that gastrin-releasing peptide or a very closely related peptide is present in areas of the rat central nervous system in which substance P has previously also been shown to be present.